1. Field of the Invention
The present invention relates, generally, to a system and method of purifying or treating a fluid and, more particularly, to a water treatment system incorporating an electrochemical device and a reservoir for delivering treated water to a point of use and a method of operating and flushing the water treatment system.
2. Description of Related Art
Water that contains hardness species such as calcium and magnesium may be undesirable for some uses in industrial, commercial and household applications. The typical guidelines for a classification of water hardness are: zero to 60 milligrams per liter (mg/l) as calcium carbonate is classified as soft; 61 to 120 mg/l as moderately hard; 121 to 180 mg/l as hard; and more than 180 mg/l as very hard.
Hard water can be softened or treated by removing the hardness ion species. Examples of systems that remove such species include those that use ion exchange beds. In such systems, the hardness ions become ionically bound to oppositely charged ionic species that are mixed on the surface of the ion exchange resin. The ion exchange resin eventually becomes saturated with ionically bound hardness ion species and must be regenerated. Regeneration typically involves replacing the bound hardness species with more soluble ionic species, such as sodium chloride. The hardness species bound on the ion exchange resin are replaced by the sodium ions and the ion exchange resins are ready again for a subsequent water softening step.
Other systems have been disclosed. For example, Dosch, in U.S. Pat. No. 3,148,687 teaches a washing machine including a water softening arrangement using ion exchange resins. Similarly, Gadini et al., in International Application Publication No. WO00/64325, disclose a household appliance using water with an improved device for reducing the water hardness. Gadini et al. teach of a household appliance having a control system, a water supply system from an external source and a softening system with an electrochemical cell. McMahon, in U.S. Pat. No. 5,166,220, teaches of a regeneration of ion exchange resin with a brine solution in a water softening process.
Electrodeionization (EDI) can be used to soften water. EDI is a process that removes ionizable species from liquids using electrically active media and an electrical potential to influence ion transport. The electrically active media may function to alternately collect and discharge ionizable species, or to facilitate the transport of ions continuously by ionic or electronic substitution mechanisms. EDI devices can include media having permanent or temporary charge and can be operated to cause electrochemical reactions designed to achieve or enhance performance. These devices also include electrically active membranes such as semi-permeable ion exchange or bipolar membranes.
Continuous electrodeionization (CEDI) is a process that relies on ion transport through electrically active media (electroactive media). A typical CEDI device includes alternating electroactive semi-permeable anion and cation selective membranes. The spaces between the membranes are configured to create liquid flow compartments with inlets and outlets. A transverse DC electrical field is imposed by an external power source through electrodes at the bounds of the compartments. In some configurations, electrode compartments are provided so that reaction product from the electrodes can be separated from the other flow compartments. Upon imposition of the electric field, ions in the liquid to be treated in one compartment, the ion-depleting compartments, are attracted to their respective attracting electrodes. The ions migrate through the selectively permeable membranes into the adjoining compartments so that the liquid in the adjoining ion-concentrating compartments become ionically concentrated. The volume within the depleting compartments and, in some embodiments, within the concentrating compartments, includes electrically active or electroactive media. In CEDI devices, the electroactive media may include intimately mixed anion and cation exchange resins. Such electroactive media typically enhances the transport of ions within the compartments and may participate as a substrate for controlled electrochemical reactions. Electrodeionization devices have been described by, for example, Giuffrida et al. in U.S. Pat. Nos. 4,632,745, 4,925,541 and 5,211,823, by Ganzi in U.S. Pat. Nos. 5,259,936 and 5,316,637, by Oren et al. in U.S. Pat. No. 5,154,809 and by Kedem in U.S. Pat. No. 5,240,579.
Other systems that can be used to demineralize water have been described. For example, Gaysowski, in U.S. Pat. No. 3,407,864, teaches of an apparatus that involves both ion exchange and electrodialysis. Johnson, in U.S. Pat. No. 3,755,135, teaches of a demineralizing apparatus using a DC potential.